[gmx-developers] virial contributions
H.J.Risselada at rug.nl
Mon Oct 9 11:51:49 CEST 2006
When looking to the code pull.c (gmx-3.3.1) I see e.g that
in the umbrella sampling part a virial contribution is
calculated from the double sum of the pull forces together
with the pulled positions relative from equilibrium (the
well of the potential). However, instead of the expected
factor -0.5 a factor of +0.5 is included while in other
parts of the code the -0.5 is included (calcvir.c).
The pressure equations implemented in gromacs is the one
directly from litterature which however also implies the
-0.5 factor in the virial.
It's by sure not unthinkable that I just overlook a minus
sign or a substraction somewhere else on the code, but on
first sight it looks to me the virial contribution of
pulling is now substracted instead of added to the
Can someone please explain me this ?
Physically I would expect the opposite, hence it's the
virial contribution added to form the virial which
represents the state of the biased ensemble.
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